Generator rotors are provided with radial slots about the periphery thereof, for receiving field or rotor windings of coils made up of a number of turns in a radially stacked arrangement, each turn or winding separated by insulation. The windings are retained in the slots by full-length wedges, with creepage blocks interposed between the wedges and the windings.
The generators currently available from the assignee are placed in three major design classifications based on the cooling medium used: air, hydrogen and liquid cooled. All hydrogen-water cooled generators use direct conductor cooling of the rotor winding for heat removal. Smaller two-pole and all four-pole generators use the radial flow design where hydrogen enters the windings through full length sub-slots and is discharged along the length of the rotor body through radial slots, machined or punched in the copper windings. The hydrogen passes from the conductors through the creepage blocks and wedges to the "air gap" between the rotor and the stator, where it is directed through the stator core to the hydrogen coolers.
At higher generator ratings, and consequently rotor body lengths, a gap-pickup diagonal-flow cooling process is employed. In this scheme, cold hydrogen is scooped up in the air gap between the rotor and stator and driven diagonally inwardly through the rotor field turns to directly remove the heat. At the bottom of the slot, the gas is turned and passes diagonally outwardly through the field turns to the air gap in the discharge stator core section. The stator core ventilation is coordinated with the rotor cooling gas flow, thus creating an in and out flow of hydrogen through the stator core, through the rotor and returning to the hydrogen cooler through the core.
The generator field windings consist of extruded copper that is drawn at a copper mill and then machined and fabricated into a usable coil. Within the last few years, these coils have been redesigned from square corner fabricated coils, to a "C" coil. The cross section of the copper to make these coils has essentially remained the same. The "C" coil has nevertheless been preferred because many benefits have been derived from that shape relating to cost, cycle time and quality. Nevertheless, in order to maintain a competitive stance in the marketplace, new copper designs are constantly being evaluated for increased performance. With the constant design changes, the cross sectional area of the copper has been increasing. When the thickness increases, the radial air cooling ducts that are machined in by a punch operation become increasingly more difficult to produce. For example, conventional punch operations may produce an unacceptable bulge in the width dimension of the copper, and it is therefore necessary to create a ventilation scheme for the increasing cross sections of the copper windings without unacceptable bulge in the width dimension.
It has also been attempted to improve the field winding ventilation or cooling by punching or forging turbulators within the radial cooling ducts. This approach, however, adds a second manufacturing operation and may, in fact, add to the bulge problem.